text: The oldest archaeological evidence of copper mining and working was the discovery of a copper pendant in northern Iraq from 8,700 BCE. The earliest substantiated and dated evidence of metalworking in the Americas was the processing of copper in Wisconsin, near Lake Michigan. Copper was hammered until it became brittle, then heated so it could be worked further. In America, this technology is dated to about 4000–5000 BCE. The oldest gold artifacts in the world come from the Bulgarian Varna Necropolis and date from 4450 BCE.
  Not all metal required fire to obtain it or work it. Isaac Asimov speculated that gold was the "first metal". His reasoning being, that, by its chemistry, it is found in nature as nuggets of pure gold. In other words, gold, as rare as it is, is sometimes found in nature as a native metal. Some metals can also be found in meteors. Almost all other metals are found in ores, a mineral-bearing rock, that require heat or some other process to liberate the metal. Another feature of gold is that it is workable as it is found, meaning that no technology beyond a stone hammer and anvil is needed to work the metal.  This is a result of gold's properties of malleability and ductility. The earliest tools were stone, bone, wood, and sinew, all of which sufficed to work gold.
  At some unknown time, the process of liberating metals from rock by heat became known, and rocks rich in copper, tin, and lead came into demand. These ores were mined wherever they were recognized.  Remnants of such ancient mines have been found all over Southwestern Asia. Metalworking was being carried out by the South Asian inhabitants of Mehrgarh between 7000 and 3300 BCE. The end of the beginning of metalworking occurs sometime around 6000 BCE when copper smelting became common in Southwestern Asia.
  Ancient civilisations knew of seven metals. Here they are arranged in order of their oxidation potential (in volts):
  *Iron     +0.44 V,
  *Tin      +0.14 V
  *Lead     +0.13 V
  *Copper   −0.34 V
  *Mercury  −0.79 V
  *Silver   −0.80 V
  *Gold     −1.50 V.
  The oxidation potential is important because it is one indicator of how tightly bound to the ore the metal is likely to be.  As can be seen, iron is significantly higher than the other six metals while gold is dramatically lower than the six above it. Gold's low oxidation is one of the main reasons that gold is found in nuggets. These nuggets are relatively pure gold and are workable as they are found.
  Copper ore, being relatively abundant, and tin ore became the next important substances in the story of metalworking. Using heat to smelt copper from ore, a great deal of copper was produced. It was used for both jewelry and simple tools. However, copper by itself was too soft for tools requiring edges and stiffness. At some point tin was added into the molten copper and bronze was developed thereby.  Bronze is an alloy of copper and tin.  Bronze was an important advance because it had the edge-durability and stiffness that pure copper lacked.  Until the advent of iron, bronze was the most advanced metal for tools and weapons in common use (see Bronze Age for more detail).
  Outside Southwestern Asia, these same advances and materials were being discovered and used around the world. People in China and Great Britain began using bronze with little time being devoted to copper. Japanese began the use of bronze and iron almost simultaneously. In the Americas it was different.  Although the peoples of the Americas knew of metals, it was not until the European colonisation that metalworking for tools and weapons became common. Jewelry and art were the principal uses of metals in the Americas prior to European influence.
  About 2700 BCE, production of bronze was common in locales where the necessary materials could be assembled for smelting, heating, and working the metal. Iron was beginning to be smelted and began its emergence as an important metal for tools and weapons. The period that followed became known as the Iron Age.